Miranda Lambert is in the best shape of her life after her recent 25-pound weight loss.

Lambert turned heads in a glittery nude evening gown at the 2014 Academy of Country Music Awards (ACM) in Las Vegas April 6.

Miranda lost 25 pounds ahead of her 30th birthday (in November 2013) because she wanted to turn over a new leaf as she entered a new decade.

"I can't use that I'm-only-in-my-20s excuse anymore about anything," she told People. "Now it's time to be responsible. I spent my 20s on a roller coaster — my yo-yo weight, working all the time and partying. I just wanted to get healthier and go into my thirties in the best shape I could be in.”

Lambert credited a portion-controlled diet and rigorous circuit-training workouts for her amazing makeover. Miranda overhauled her diet by cutting portion sizes and substituting her usual breakfast of bacon and eggs with a nutrient-rich green juice. When she does indulge, she eats only half of what's on her plate.

Smaller portions right from the start [help]. I haven't given up everything! I try to just cut everything in half. Instead of steak for dinner, I might have chicken and a baked sweet potato.”

The physical transformation mirrored internal changes in her, including becoming more self-confident and more responsible about the direction of her career, health, and life. The result has been a calmer, more centered, Miranda.

"I feel like people have accepted me for who I am, with all the craziness, loudness and fire," said Lambert, who has sold more than five million albums. "At some point, you calm down. I'm happy. I'm more settled. I've put down roots."

Miranda, who's married country superstar Blake Shelton, made headlines after debuting her slimmed-down physique at the 2013 CMA Awards. She was shocked at the amount of attention she received after the weight loss, because she didn't think anyone would notice.

“I didn’t know until [the CMA Awards] that people were noticing," she said. "But you want people to notice when you’ve worked hard and feel good. That’s part of the reward. It’s a great motivator."

Miranda recently slammed rumors she underwent weight-loss surgery to lose over 25 pounds, saying eating less and exercising more helped her lose over two dress sizes.

"I did not have surgery to lose weight," she said. "That is ridiculous. I lost my weight the healthy and good-old fashioned way: Watching what I eat and working out with my trainer Bill Crutchfield. We do cardio and a lot of circuit-training."

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Samantha Chang is the co-owner of www.theimproper.com., an arts and entertainment website in New York City. A graduate of the University of Pennsylvania, Samantha enjoys running, cycling and taking photos. Contact her at schang@theImproper.com.